type DescribableFunction = {
    description: string
    (someArg: number): boolean
}

function doSomething(fn: DescribableFunction) {
    console.log(fn.description + " returned " + fn(6))
}

function myFunc(someArg: number) {
    return someArg > 3
}

myFunc.description = 'default description'
doSomething(myFunc)